Process for activating aluminum anode



United States Patent Ofifice 3,336,163 Patented Aug. 15, 1967 3,336,163 PROCESS FOR ACTIVATING ALUMINUM AN ODE Wade Wolfe, Jr., Mount Carmel, Conn., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Filed Sept. 24, 1963, Ser. No. 311,214 7 Claims. '(Cl. 136-420) The present invention relates to a process for activating aluminum containing anodes and to the improved aluminum containing anode thereby obtained.

Because of their numerous excellent properties, aluminum-containing anodes have been widely used in a variety of applications, for example, aluminum-containing anodes may be advantageously used (1) in primary electric batteries suitable for use with liquid electrolytes, such as aqueous electrolytes and especially sea water, (2) as sacri ficial aluminum-containing anodes in conjunction with a metallic cathode which thereby receives substantial protection against corrosion and (3) in primary cells of the dry type, with the aluminum-containing anode also serving as the container for the cell.-

Particularly advantageous are the numerous aluminum base alloys especially formulated to provide good anodic characteristics. Examples of such aluminum-containing alloys may be found in United States patent application Ser. No. 251,024, filed Jan. 14, 1963, now US. Patent 3,189,486, which relates to a highly efiicient metal anode comprising an aluminum base alloy containing at least 90 percent aluminum and between 0.04 and 0.5 percent tin.

One disadvantage, however, of aluminum-containing anodes which has limited their eifectiveness for numerous applications is the relatively long periods of time required for these anodes to achieve full power output. For example, the aluminum-tin alloys disclosed in United States patent application Ser. No. 251,024, referred to above, achieve full power output after approximately one minutes operation. This disadvantage is especially significant when aluminum-containing alloys are utilized as the anodes of sea water batteries containing, for example, silver chloride cathodes. These batteries are activated by filling with sea water and must achieve full power output in a matter of seconds, especially in view of relatively short life of the battery, often as little as six minutes.

The magnesium alloys conventionally used as anodes in sea water batteries generally achieve fullpower output after approximately 15 seconds. However, the aluminumcontaining anodes have numerous highly desirable advantages over the magnesium anodes and, therefore, it is highly desirable to simply and conveniently overcome the foregoing disadvantage, namely, the relatively slow activation characteristics of aluminum-containing anodes.

The relatively slow activation rate of aluminum-containing anodes is believed to be due to the natural surface oxide and hydrated oxide corrosion products that form -on the anodes during standing in ordinary air. Abrasive removal of the corrosion products is effective in increasing the activation rate; however, the corrosion product quickly reforms when the aluminum surface is allowed to remain in air, even, for example, after 24 hours in a desiccator.

It is, therefore, an object of the present invention to provide a process for activating aluminum-containing anodes and to provide an improved anode.

It is a further object of the present invention to provide an improved aluminum-containing anode, and an improved process for obtaining same, said anode being characterized by rapid achievement of full power output.

It is a still'further object of the present invention to of the anode.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention it has now been found that the foregoing objects and advantages may be readily obtained and a process for activatin aluminum-containinganodes provided which comprises: contacting a substantially oxide free surface of an aluminumcontaining anode for at least 0.1 second with a metal salt of an inorganic acid and preferably with a dilute solution of a metal salt of an inorganic acid. The improved activated anode of the present invention comprises an aluminous anode coated with a metallic salt of an inorganic acid on the surface of the aluminum or covered with an adsorbed film of a metallic salt of an inorganic acid on the surface of the aluminum.

In accordance with the process of the present invention it has been surprisingly found that the foregoing simple and expeditious process overcomes the disadvantages in the use of aluminum-containing anodes and achieves full power output in a relatievly short period of time, even after storage in air. Especially surprising and unexpected in accordance with the present invention is that the aluminum containing anode treated in accordance with the present invention actually attains improved current density.

The process of the present invention is effective in improving the anodic characteristics of any aluminum base alloy. The critical requirement is that the alloy contain a major proportion of aluminum, i.e., greater than 50 percent aluminum, since the aluminum is the factor which retards the rapid attainment of full power output. Exemplificative anodic material include, but are not limited to, pure aluminum, aluminum base alloys containing varying proportions of alloying ingredients, such as, for example, up to 10 percent zinc to obtain improved galvanic activity, e.g., alloy 7072, and also, for example, aluminum base alloys containing at least percent aluminum and from 0.04 to 0.5 percent tin as discussed in United States patent application Ser. No. 251,024. Preferably, the tin is retained in solid solution to the maximum degree, i.e., about 0.1 percent, with the excess tin, or a suitable third ingredient, being provided as taught in co-pending application Ser. No. 60,166, filed Oct. 3, 1960, now US. Patent 3,180,728, to improve uniformity of corrosion and to improve anodic efficiency.

The preferred manner of preparing the alloys in the above-identified co-pending patent applications is to heat the aluminum-tin sample at elevated temperatures, e.g., between about 570-640 C. for a sufficient period of time to dissolve the maximum amount of tin and to redistribute excess tin or other alloying additions in a coarse, particulate form which produces maximum uniformity of attack and power efiiciency. Generally, the heating period within the preferred temperature range may vary between 15 minutes and 2.4 hours. After the heating period the sample is cooled rapidly, for example, by immersion in a large volume of water at ambient temperatures. For simplicity, this treatment may be termed homogenization treatment.

It is preferred in accordance with the process of the present invention to bring the metallic salt into contact with the surface of the aluminum containing anode from which the natural oxide has been freshly removed. Oxides and hydrated oxides can be mechanically removed by conventional techniques such as wire brushing, abrasive wheels or papers or by directing an abrasive to the surface in a stream of fluid, either gaseous or liquid. Oxides and hydrated oxides can also be removed by electrochemical or by chemical means such as solution by acids or bases. The oxide free surface of the aluminum containing anode can be contacted with liquid salts, gaseous salts or solutions of metallic salts. The metal salt can also be formed at the surface by first depositing a metal on the surface by such means as galvanic or electrochemical plating or vapor plating, and then reacting the deposited metal with an appropriate anion.

It is preferred in accordance with the process of the present invention that the metallic salt is brought into contact with the surface of an aluminum-containing anode at the time the natural oxide is removed from the anode surface. This can be accomplished by abrading the anode surface immersed in a metal salt solution. More conveniently, it is preferred to dissolve the natural oxide film with an acidic or basic solution containing a dissolved metallic salt. Most acidic or basic solutions may be conveniently used, for example, hydrochloric acid, phosphoric acid, nitric acid, sulfuric acid, acetic acid and citric acid or bases such as sodium hydroxide, potassium hydroxide and calcium hydroxide.

It is preferred in accordance with the present invention to utilize dilute aqueous acidic solutions, preferably having a pH less than 3 or dilute aqueous basic solutions, preferably having a pH greater than 10. It is desirable that the acidic or basic solution should be sufficiently reactive to dissolve the natural oxide from an anode surface within a reasonable period of time at temperatures up to the atmospheric boiling point of the solution.

In the preferred embodiment the acidic or basic treatment step is combined with the step of contacting the anode with the metallic salt. Thus, in the preferred embodiment the aluminum anode is contacted with an acidic or basic solution containing the desired metallic salt. In this embodiment, naturally, the solution should be such as will not interact adversely with the metallic salt.

In accordance with the present invention it is preferred to use the inorganic acid salts of the metals in Groups I, II, III and IV of the periodic arrangement of the elements, for example, halide, nitrate, phosphate, carbonate, aluminate and sulfate salts of these metals. In the preferred embodiment the metallic salt must have at least a slight solubility in water or in the acidic or basic solution.

The metallic salt solution should have a concentration of at least one part per million. Normally, there is no advantage to use solutions in which the metallic salt concentration exceeds one normal.

In accordance with the present invention the time of contact is not especially critical, it being required only that the oxide free surface of an aluminum anode be in contact with the metal salt solution for at least 0.1 second. A sufficient time of contact will normally transpire during manipulations required to remove the natural oxide from the aluminum anode surface in the presence of the metal salt solution. For example, when the metal salt is combined with a basic solution at pH 10, 30 minutes may be required at ambient temperatures, 3 minutes at 150 F. and one minute at the atmospheric boil point to dissolve the natural oxide from the aluminum anode surface. Of course, the time required to dissolve a natural oxide film can be shortened by abrading the aluminum anode surface prior to contact with the acidic or basic solution or by adjusting the pH of the acidic solution to a value less than 3 or the pH of the basic solution to a value greater than 10.

The particular method of contacting the anode with both the acid-base solution and the metallic salt solution is not especially critical and any conventional method, such as spraying, brushing, coating, dipping, etc., may be employed. Naturally, for convenience it is preferred to simply immerse the anode in the solution for the desired period of time.

In general, it has been found that salts of metals below aluminum in the electromotive series, that is, more electropositive than aluminum, for example, will provide a more active aluminum surface when used in combination with an acidic solution treatment. On the other hand, it has been found that salts of more electronegative metals, i.e., higher than aluminum in the electromotive series which are preferred, for example, will give more active aluminum surface when used in combination with an alkaline or basic solution treatment. Naturally, improvement is obtained with either of these types of metals in both alkaline or the acidic solution treatment.

In addition, it has been found that a metallic salt can be selected so that its aqueous solution is sufficiently acid or basic to provide the acid or basic treatment and simultaneously chemically treating the aluminum surface so as to improve and retain galvanic activity. In other words the acid or basic solution treatment may conveniently be dispensed with and still obtain significant improvements or may be combined into the metal salt treatment step or a metal salt may be selected which inherently provides a desired acid or basic solution treatment step.

The process of the present invention will be more readily apparent from a consideration of the following illustrative examples.

EXAMPLE 1 An untreated aluminum alloy sheet composed of high purity aluminum and 0.3 percent tin will produce 0.825 amp at an apparent current density of 1.1 amps/sq. in. when galvanically operating in an AU 3.4% NaCl solution/AgCl-Ag cell; however, 180 seconds are required before this level of performance is achieved. The activation time and galvanic current of this A10.3% Sn alloy sheet was improved by etching for 15 minutes in a 0.1 M solution of trisodium phosphate, pH 12.4, at room temperature followed by rinsing and air drying. Improvement in performance is shown in the following table which gives the time in seconds which elapses before different levels of current density were achieved.

Another specimen of high purity aluminum-0.3% tin alloy, as described in Example 1, was treated by immersion for 15 minutes in a 0.1 M barium chloride solution which had been adjusted to a pH of 12.9 by adding sodium hydroxide. In the AU 3.4% NaCl solution/AgCl- Ag cell, the activation of the barium chloride treated specimen was improved as indicated by the following table showing time in seconds to produce different levels of current density.

TABLE 2 Time Required to Achieve Apparent Current Density in amps/sq. in. Alloy 0. 9 1.0 1.1 Max. Current Density Untreated Al-O.3% 52 sec- 65 see. see. 1.13 in sec.

S11 alloy. BaClz treated Al-0.3% 15 see--- 23 sec". 58 sec... 1.16 in 180 see.

Sn alloy.

EXAMPLE 3 In other cell designs, high purity aluminum-0.3% tin alloy will perform in the AU 3.4% NaCl solution/AgCl- Ag cell at lower current densities. A1-0.3% Sn sheet was abraded and then stored for 65 hours in a desiccator before being placed in an Al/3.4% NaCl solution/AgCl- Ag cell where it was found to produce 0.9 amp. at an apparent current density of 0.9 amp/sq. in. However, 120 seconds elapsed before reaching 0.9 amp/sq. in. and the current density was only 0.5 amp/sq. in after six seconds. Another specimen from the same sheet was etched for 30 seconds in dilute hydrochloric acid and then immersed in 0.1 stannous chloride solution for five seconds where tin plated on the aluminum surface. EX- cess tin was removed by a 60 second etch in dilute hydrochloric acid after which the specimen was rinsed and dried. In the Al/3.4% NaCl solution/AgCl-Ag cell, the stannous chloride treated aluminum alloy produced 0.88 amp./ sq. in. within six seconds.

EXAMPLE 4 A specimen of high purity aluminum0.3% tin alloy was etched for 60 seconds in a combined solution consisting of 0.1 M stannous chloride and weak hydrochloric acid. In the Al/3.4% NaCl solution/AgCl-Ag cell, similar results to those described in Example 3 were obtained.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. A process for activating an aluminum containing anode to reduce the time needed to achieve full power output which comprises: providing an aluminum containing anode; dissolving the oxide from the surface of said anode while simultaneously activating said anode by contacting said anode for at least 0.1 second with an aqueous solution selected from the group consisting of an acidic solution and a basic solution, said solution containing a metallic salt of an inorganic acid, and placing said anode in a galvanically operating primary cell as the anode thereof, thereby achieving full power output in less than 120 seconds.

2. A process according to claim 1 wherein the concentration of metallic salt in said solution exceeds one part per million and wherein the metallic salt concentration is less than one normal.

3. A process according to claim 1 wherein said acidic solution has a pH less than 3 and wherein said basic solution has a pH in excess of 10.

4. A process according to claim 1 wherein said metallic salt of an inorganic acid contains a metal selected from the group consisting of Groups I, II, III and IV of the periodic table of elements and wherein said metallic salt of an inorganic acid contains a salt selected from the group consisting of halide, nitrate, phosphate, carbonate, aluminate and sulfate.

5. A process according to claim 1 wherein said solution contains a material selected from the group consisting of hydrochloric acid, phosphoric acid, nitric acid, sulfuric acid, acetic acid, citric acid, sodium hydroxide, potassium hydroxide and calcium hydroxide.

6. A process according to claim 1 wherein said aluminum base alloy anode contains at least 90 percent aluminum and between 0.04 and 0.5 percent tin.

7. A process according to claim 1 wherein said solution contains trisodium phosphate.

References Cited UNITED STATES PATENTS 2,437,220 3/1948 Bonwitt 204-148 2,654,701 10/1953 Calderon et al.

2,714,066 7/1955 Jewett et al 117-l27 X 2,796,371 6/1957 Ostrander et al. 148-6.27 2,883,311 4/1959 Halpert 1486.27 3,113,051 12/ 1963 Pimbley et a1. 148-627 3,180,728 4/1965 Pryor et a1. -138 3,227,644 1/ 1966 Rutemiller 204197 3,247,026 4/1966 Switzer 148-6.27

JOHN H. MACK, Primary Examiner. T. TUNG, Assistant Examiner. 

1. A PROCESS FOR ACTIVATING AN ALUMINUM CONTAINING ANODE TO REDUCE THE TIME NEEDED TO ACHIEVE FULL POWER OUTPUT WHICH COMPRISES: PROVIDING AN ALUMINUM CONTAINING ANODE; DISSOLVING THE OXIDE FROM THE SURFACE OF SAID ANODE WHILE SMULTANEOUSLY ACTIVATING SAID ANODE BY CONTACTING SAID ANODE FOR AT LEAST 0.1 SECOND WITH AN AQUEOUS SOLUTION SELECTED FROM THE GROUP CONSISTING OF AN ACIDIC SOLUTION AND A BASIC SOLUTION, SAID SOLUTION CONTAINING A METALLIC SALT OF AN INORGANIC ACID, AND PLACING SAIC ANODE IN A GALVANICALLY OPERATING PRIMARY CELL AS THE ANODE THEREOF, THEREBY ACHEIVING FULL POWER OUTPUT IN LESS THAN 120 SECONDS. 